(a) Field of the Invention
This invention relates to a process for synthesizing cellulose aminomethanate which has utility in the manufacture of sausage casing and other cellulose products.
(b) History of the Prior Art
Cellulose xanthate, dissolved as viscose, has been utilized for many years in the manufacture of regenerated cellulose film which has particular utility as sausage casings. With the increase in environmental awareness, concerns have been raised to the environmental management of flammable and toxic reactants and by-products of the viscose manufacturing process. The rapidly escalating cost of by-product management, coupled with the intrinsic costs of additives, which are necessary when utilizing viscose for regenerated cellulose sausage casings, has forced the sausage casing industry to search for viable alternatives to current viscose manufacturing processes.
One alternative, which has more recently been the focus of research for possible replacement of the viscose process in the sausage casing industry is the use of ammonia derivatives, such as urea, reacted with cellulose to form a soluble cellulose derivative. The use of such materials is preferable as byproducts are easily managed and do not appear to represent significant environmental impact. U.S. Pat. Nos. 1,771,461; 2,134,825; and 2,129,708 comprise some of the early work in that technology demonstrating that film products are obtainable that have utility. Though the final products formed showed potential for use as a film, it wasn't until U.S. Pat. No. 4,789,006 that a product was produced having a combination of properties commercially acceptable for use as sausage casings.
Various different terminology has been used to describe the products of cellulose and urea, such as cellulose aminoformates, cellulose carbamates, cellulose aminomethanoates and cellulose aminomethanates as adopted in U.S. Pat. No. 4,789,006. To deter further confusion, the products formed with cellulose and urea as presented in the above patents and hereinafter will be referred to as cellulose aminomethanates.
Even though a cellulose aminomethanate product can now be made which is suitable for use as a sausage casing, problems still exist in the manufacturing process occasioned by the difficulty of removing prior art carriers, such as sodium hydroxide, used to obtain uniform distribution of the urea through the cellulose structure prior to the formation of the cellulose aminomethanate. This need for uniform distribution of the urea is disclosed in U.S. Pat. No. 4,404,369 and achieved by using liquid ammonia which can be subsequently removed by volatilization. However, liquid ammonia is highly volatile, toxic, pungent, forms explosive mixtures with air and requires excessive refrigeration and special equipment for safe handling and recovery.
In a later process, disclosed in European Patent Application No. 85890246.3 (1985), uniform distribution was achieved by using high concentrations of sodium hydroxide which was then washed out with neutral aqueous urea. Such process, however, requires the handling of large volumes of liquid and creates associated recovery problems.
It is an object of this invention to improve the distribution of urea throughout the cellulose structure prior to the formation of cellulose aminomethanate.
It is another object of this invention to provide an improved cellulose aminomethanate material having uniform distribution of aminomethanate substituent.
It is a further object of this invention to provide a convenient means for processing cellulose which has been steeped in sodium hydroxide.
It is a still further object to provide a means to reduce and/or eliminate the growth in volume of extracting liquids for successive batches of urea-alkali steeped pulps.
It is still another object to provide a means to allow recycle of alkali and urea used for steeping.